1. Field of the Invention
The present invention relates to extending the dynamic range of a television camera and more particularly to a wide dynamic range imaging apparatus that permits scenes having a wide range of luminance to be captured and an image signal processing method for use therewith
2. Description of the Related Art
With conventional cameras using imaging elements such as charge coupled devices (CCDs), the amount of incident light is controlled to within a certain range because of limitations on their charge accumulation capacity and their charge accumulation characteristics. In outdoor shooting, therefore, the dynamic range cannot be obtained which allows the luminance variations of scenes to be captured successfully, which will lead to a problem of image quality.
For this reason, in the prior art, the dynamic range has been extended through the use of the electronic shutter function of the imaging element; that is, by capturing the image of a scene at high and low shutter speeds and processing the resultant image signals.
An electronic camera adapted to increase the dynamic range of the imaging element by combining image data obtained using different controlled parameters during two successive electronic shutter intervals is disclosed in, for example, U.S. Pat. No. 4,647,975.
However, in the conventional electronic cameras, the low and high shutter speeds and the image data combination ratio are fixed. The above method by which images captured several times at different shutter speeds are combined is effective in increasing the dynamic range of devices adapted to capture still images but is not suitable for devices adapted to capture the images of moving objects, such as supervisory cameras